Today, many people all over the world use several different telecommunication devices such as PSTN desktop phones, IP desktop phones, PC softphones and mobile phones etc. Especially mobile phones and IP telephony (IP desk phones and PC softphones) have become popular the recent years. Mobile phones are advantageous as the user can move around while having a conversation with other call participants. PSTN and IP telephony is advantageous as it often provides telephony at low rates and good audio quality. When a user is in a call on the PSTN or IP telephone and must leave his desk, maybe for driving home or to a meeting, he must end the call, and continue it on the mobile phone. This is cumbersome and time consuming. He may be able to transfer the call, but this requires manual interaction. In addition, the situation, where a user is arriving at his desk while having a phone call on his mobile phone, he may wish to transfer the call to the PSTN or IP desk phone or PC softphone, which also requires manual interaction.
US 2011/0207447 (Plantronics Inc) discloses a headset system according to the preamble, which system makes it possible for a user to seamlessly transfer a call from a first telecommunication device to a second telecommunication device by entering a call transition mode of the headset.